Toilet Sometimes Will Not Flush My Girlfriends Son Is 6. And He Sometimes "forgets" To Flush The Toilet. What Can We Do To Make Sure He Does?

My girlfriends son is 6. And he sometimes "forgets" to flush the toilet. What can we do to make sure he does? - toilet sometimes will not flush

We put a sign above the toilet that he helped write, too. It stands in the middle of the night to urinate and sometimes forget ... I do not understand that sometimes, cuz that is now, but how sleep twice a week and not drag the Damn Channel. In this way, your mother and me very disappointed. What can we do to make you remember?
We thought that the sign of the weekly change and the publication of another due to the change.
I hope the wonderful people who can help with some ideas.
Thank you again.
B.